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Date:   Thu, 22 Sep 2022 10:02:42 +0800
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Subject: Re: [PATCH v4 3/6] iommu: Add return value rules to attach_dev op and
 APIs
Content-Language: en-US
To:     Nicolin Chen <nicolinc@nvidia.com>, joro@8bytes.org,
        suravee.suthikulpanit@amd.com, will@kernel.org,
        robin.murphy@arm.com, robdclark@gmail.com, dwmw2@infradead.org,
        agross@kernel.org, bjorn.andersson@linaro.org,
        matthias.bgg@gmail.com, orsonzhai@gmail.com,
        baolin.wang@linux.alibaba.com, zhang.lyra@gmail.com,
        jean-philippe@linaro.org, sricharan@codeaurora.org
References: <cover.1663744983.git.nicolinc@nvidia.com>
 <8c3dbf153b63a3002a46bab6e707c63fd8635bb8.1663744983.git.nicolinc@nvidia.com>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <8c3dbf153b63a3002a46bab6e707c63fd8635bb8.1663744983.git.nicolinc@nvidia.com>
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Precedence: bulk

On 9/21/22 4:23 PM, Nicolin Chen wrote:
> Cases like VFIO wish to attach a device to an existing domain that was
> not allocated specifically from the device. This raises a condition
> where the IOMMU driver can fail the domain attach because the domain and
> device are incompatible with each other.
> 
> This is a soft failure that can be resolved by using a different domain.
> 
> Provide a dedicated errno EINVAL from the IOMMU driver during attach that
> the reason why the attach failed is because of domain incompatibility.
> 
> VFIO can use this to know that the attach is a soft failure and it should
> continue searching. Otherwise, the attach will be a hard failure and VFIO
> will return the code to userspace.
> 
> Update kdocs to add rules of return value to the attach_dev op and APIs.
> 
> Suggested-by: Jason Gunthorpe<jgg@nvidia.com>
> Signed-off-by: Nicolin Chen<nicolinc@nvidia.com>
> ---
>   drivers/iommu/iommu.c | 22 ++++++++++++++++++++++
>   include/linux/iommu.h | 12 ++++++++++++
>   2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 3a808146b50f..1d1e32aeaae6 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1975,6 +1975,17 @@ static int __iommu_attach_device(struct iommu_domain *domain,
>   	return ret;
>   }
>   
> +/**
> + * iommu_attach_device - Attach a device to an IOMMU domain

Normally we say "attach an iommu domain to a device/group ...".

Best regards,
baolu